Hmm. Admittedly I hadn’t properly read the API documentation. My aim was to match the rule results with what I see on my Octopus dashboard, and the code as it was gave me a 1 hour offset.
The last part of this statement might be relevant
We strongly recommend that timezone information is included on all datetime parameters. If no timezone information is included, the “Europe/London” timezone will be assumed and results may vary between GMT and British Summer Time.